Chapter 13

DIONAEA MUSCIPULA.

Structure of the leaves--Sensitiveness of the filaments--Rapid movement of the lobes caused by irritation of the filaments--Glands, their power of secretion--Slow movement caused by the absorption of animal matter--Evidence of absorption from the aggregated condition of the glands--Digestive power of the secretion--Action of chloroform, ether, and hydrocyanic acid--The manner in which insects are captured--Use of the marginal spikes--Kinds of insects captured--The transmission of the motor impulse and mechanism of the movements-- Re-expansion of the lobes.

THIS plant, commonly called Venus' fly-trap, from the rapidity and force of its movements, is one of the most wonderful in the world.* It is a member of the small family of the Droseraceae, and is found only in the eastern part of North Carolina, growing in damp situations. The roots are small; those of a moderately fine plant which I examined consisted of two branches about 1 inch in length, springing from a bulbous enlargement. They probably serve, as in the case of Drosera, solely for the absorption of water; for a gardener, who has been very successful in the cultivation of this plant, grows it, like an epiphytic orchid, in well-drained damp moss without any soil. The form of the bilobed leaf, with its foliaceous footstalk, is shown in the accompanying drawing (fig. 12).

* Dr. Hooker, in his address to the British Association at Belfast, 1874, has given so full an historical account of the observations which have been published on the habits of this plant, that it would be superfluous on my part to repeat them.

'Gardener's Chronicle,' 1874, p. 464.

The two lobes stand at rather less than a right angle to each other. Three minute pointed processes or filaments, placed triangularly, project from the upper surfaces of both; but I have seen two leaves with four filaments on each side, and another with only two. These filaments are remarkable from their extreme sensitiveness to a touch, as shown not by their own movement, but by that of the lobes. The margins of the leaf are prolonged into sharp rigid projections which I will call spikes, into each of which a bundle

FIG. 12. (Dionaea muscipula.) Leaf viewed laterally in its expanded state.

of spiral vessels enters. The spikes stand in such a position that, when the lobes close, they inter-lock like the teeth of a rat-trap. The midrib of the leaf, on the lower side, is strongly developed and prominent.

The upper surface of the leaf is thickly covered, excepting towards the margins, with minute glands of a reddish or purplish colour, the rest of the leaf being green. There are no glands on the spikes, or on the foliaceous footstalk, The glands are formed of from twenty to thirty polygonal cells, filled with purple fluid. Their upper surface is convex. They stand on very short pedicels, into which spiral vessels do not enter, in which respect